Andrew Ross Sorkin has a lengthy discussion of the complexities of the Volcker rule, which bans proprietary trading by banks that hold government guaranteed deposits. The point of the rule is that banks should not be taking risks with taxpayers' money.
While Sorkin ultimately comes down in favor of the rule, he neglects to point out that until 1999 there was a much stricter rule in the form of the Glass Steagall separation between commercial and investment banking. Up to that point, investment banks like Goldman Sachs and Merill Lynch could do whatever trading they wanted. In principle they were not putting government money at risk, since they did not enjoy protection from the Fed and the FDIC. These banks also made large profits.
If banks now find the Volcker rule to be too onerous, as they claim, then there is no obvious reason they could not just separate their investment banking and commerical banking divisions so that they are again independent companies. It is certainly understandable that the banks would prefer to be able to gamble with taxpayers money (who wouldn't?), but they really don't have much of a case.
btw, Sorkin begins his piece with a paean to Volcker:
"It is hard to disagree with Paul A Volcker.
"But I will.
"On Monday, Mr. Volcker, the former Federal Reserve chairman who almost single-handedly rescued the United States from the stagflation crisis of the late 1970s."
Whether or not one agrees with the interest rate policies that Volcker used to slow inflation, which gave us double digit unemployment, it is a bit hard to describe Volcker as uniquely talented. All wealthy countries saw a sharp decline in their inflation rates at the beginning of the 80s. This suggests that Mr. Volcker's skills were not needed to bring inflation down.